Post on 03-Apr-2018
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Urban Stormwater Management
in the United States Therapidconversionoflandtourbanandsuburbanareashasprofoundlyaltered
how water ows during and following storm events, putting higher volumes of water and
more pollutants into the nations rivers, lakes, and estuaries. These changes have degraded
water quality and habitat in virtually every urban stream system. The Clean Water Act
regulatory framework for addressing sewage and industrial wastes is not well suited to
the more difcult problem of stormwater discharges. This report calls for an entirely new
permitting structure that would put authority and accountability for stormwater discharges
at the municipal level. A number of additional actions, such as conserving natural areas,
reducing hard surface cover (e.g., roads and parking lots), and retrotting urban areas with
features that hold and treat stormwater, are recommended.
Stormwater has long been regarded as a
major culprit in urban ooding, but only
in the past 30 years have policymakers
appreciated its signicant role in degrading the streams,
rivers, lakes, and other waterbodies in urban and
suburban areas. Large volumes of rapidly moving
stormwater can harm species habitat and pollute
sensitive drinking water sources, among other impacts.
Urban stormwater is estimated to be the primary
source of impairment for 13 percent of assessed rivers,
18 percent of lakes, and 32 percent of estuariessignicant numbers given that urban areas cover only 3
percent of the land mass of the United States.
Urbanizationthe conversion of forests and
agricultural land to suburban and urban areasis
proceeding at an unprecedented pace in the United
States. Stormwater discharges have emerged as a problem because the
ow of water is dramatically altered as land is urbanized. Typically, vegetation and topsoil are
removed to make way for buildings, roads, and other infrastructure, and drainage networks are
installed. The loss of the water-retaining functions of soil and vegetation causes stormwater to
reach streams in short concentrated bursts. In addition, roads, parking lots, and other impervious
surfaces channel and speed the ow of water to streams. When combined with pollutants from
lawns, motor vehicles, domesticated animals, industries, and other urban sources that are pickedup by the stormwater, these changes have led to water quality degradation in virtually all urban
streams.
In 1987 Congress wrote a new section into the Clean Water Acts National Pollutant Discharge
Elimination System to help address the role of stormwater in impairing water quality. This system,
which is enforced by the U.S. Environmental Protection Agency (EPA), has focused on reducing
pollutants from industrial process wastewater and municipal sewage dischargespoint sources
of pollution that are relatively straightforward to regulate. Under the new stormwater program,
Photo by Roger Bannerman
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the number of permittees in the National Pollutant
Discharge Elimination System has ballooned from
about 100,000 to more than 500,000, to include
stormwater permittees from municipal areas, industry,
and construction sites one acre or larger. Not only do
stormwater permittees vastly out number wastewater
permittees, it is much more difcult to collect and treat
stormwater than wastewater.In light of these challenges, EPA asked the
National Research Council to review its stormwater
program, considering all entities regulated under the
program (i.e., municipal, industrial, and construction).
The report nds that the stormwater program will
require signicant changes if it is to improve the
quality of the nations waters. Fortunately, there are
a number of actions that can be taken. The report
concludes that the course of action most likely to halt
and reverse degradation of the nations waterways
would be to base all stormwater and other wastewater
discharge permits on watershed boundaries instead ofpolitical boundaries, which is a radical shift from the
current structure.
The Challenges of Regulating Stormwater
One of the problems in managing stormwater
discharge is that it is being addressed so late in the
development of urban areas. Historically, stormwater
management has meant ood controlby moving
water away from structures and cities as fast as
possible. Ideally, stormwater discharges would be
regulated through direct controls on land use, strictlimits on both the quantity and quality of stormwater
runoff into surface waters, and rigorous monitoring
of adjacent waterbodies to ensure that they are not
degraded by stormwater discharges. Future land
use development would be controlled to minimize
stormwater discharges. Products or sources that
contribute pollutants through stormwaterlike de-icing
materials, fertilizers, and vehicular exhaustwould be
regulated by EPA at a national level to ensure that the
most environmentally benign materials are used.
The current regulatory scheme lacks many
of these attributes. EPAs program has monitoring
requirements that are so benign as to be of little use for
the purposes of program compliance. Most dischargers
have no measurable, enforceable requirements.
Instead, the stormwater permits leave a great deal of
discretion to the regulated community to set their own
standards, develop their own pollution control schemes,
and to self-monitor. Current statistics on the states
implementation of the stormwater program, compliance
with stormwater requirements, and the ability of states
and EPA to incorporate stormwater permits with
pollution limits are uniformly discouraging.Signicant changes to the current regulatory
program are necessary to provide meaningful
regulation of stormwater dischargers in the future.
One idea is to focus the stormwater program less
on chemical pollutants in stormwater and more on
problems associated with increased volumes of water.
Some states have used ow volumes as a metric
for controlling and reducing stormwater discharge;
other regulators have used the extent of hard surfaces
(impervious cover) as a proxy for stormwater
pollutants. These substitutes for the traditional focus
on the discharge of pollutants have great potentialas stormwater management tools because they provide
specic and measurable targets. At the same time,
they focus regulators on the problems of increased
water volume, which include a condition known as
Urban Stream Syndrome (see image above).
In addition, the federal government should
provide more nancial support to state and local efforts
to regulate stormwater. Today, the stormwater program
still receives much less funding than the wastewater
program despite having many more permittees.
The Case For Watershed PermittingThe report concludes that the most likely way
to halt and reverse damage to waterbodies is through
a substantial departure from the status quonamely
a watershed permitting structure that bases all
stormwater and other wastewater discharge permits on
watershed boundaries instead of political boundaries.
Watershed-based permitting is not a new concept, but
it has been attempted in only a few communities.
High volumes of stormwater discharge have badly
damaged this stream near Philadelphia, which is
suffering from Urban Stream Syndrome. Photo by
Chris Crockett, City of Philadelphia Water Department.
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The proposed watershed permitting structure
would put both the authority and accountability
for stormwater discharges at the municipal level.
A municipal lead permittee, such as a city, would
work in partnership with other municipalities in the
watershed as co-permittees. Permitting authorities
(designated states or, otherwise, EPA) would adopt a
minimum goal in every watershed to avoid any furtherloss or degradation of designated benecial uses in the
watersheds component waterbodies and additional
goals in some cases aimed at recovering lost benecial
uses. Permittees, with support by the states or EPA,
would then conduct comprehensive impact source
analyses as a foundation for targeting solutions.
The approach gives municipal co-permittees
more responsibility, with commensurately greater
authority and funding, to manage all of the sources
discharging to the waterbodies comprising the
watershed. The report also outlines a new monitoring
program structured to assess progress toward meetingobjectives, diagnosing reasons for any lack of
progress, and determining compliance by dischargers.
The proposal further includes market-based trading
of credits among dischargers to achieve overall
compliance in the most efcient manner, and adaptive
management to determine additional actions if
monitoring demonstrates failure to achieve objectives.
As a rst step to taking the proposed program
nationwide, a pilot program is recommended
that will allow EPA to work through some of the
more predictable impediments to watershed-based
permitting, such as the inevitable limits of an urbanmunicipalitys authority within a larger watershed.
Short of adopting watershed-based permitting,
other smaller-scale changes to the EPA stormwater
program are possible. The report recommends that
EPA integrate the three different permitting types so
that construction and industrial sites come under the
jurisdiction of their associated municipalities.
Stormwater Management Approaches
Even in the absence of regulatory changes, there
are many stormwater management approaches that
can be used to prevent, reduce, and treat stormwaterows. Central to the EPA Stormwater Program is the
requirement for permittees to develop stormwater
pollution prevention plans that include stormwater
control measures. When designed, constructed, and
maintained correctly, stormwater control measures
have been demonstrated to reduce runoff volume
and peak ows and to remove pollutants. A classic
example is the removal of lead from gasoline, which
has reduced lead concentrations in stormwater by at
least a factor of four.
Stormwater control measures are grouped
in two categories: nonstructural and structural.Nonstructural stormwater control measures include
a wide range of actions that can reduce the volume
of runoff and pollutants from a new development.
Examples include the use of products that contain less
pollutants; improved urban design, for example, of
new developments that have fewer hard surfaces; the
disconnection of downspouts from hard surfaces to
instead connect with porous surfaces; the conservation
of natural areas; and improved watershed and land use
planning.
Structural stormwater control measures are
designed to reduce the volume and pollutants of smallstorms by the capture and reuse of stormwater, the
inltration of stormwater into porous surfaces, and
the evaporation of stormwater. Examples include
rainwater harvesting systems that capture runoff
There are many innovative approaches to stormwater management that can be applied in urban and suburban areas.
Chicagos City Hall (left) was retrotted with a green roof to capture stormwater. Photo courtesy CDF Inc. The
downspoutings on the house (right) drain onto a porous surface instead of onto a driveway. Photo by William Wenk.
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Committee on Reducing Stormwater Discharge Contributions to Water Pollution:Claire Welty, (Chair),
University of Maryland, Baltimore County; Lawrence E. Band, University of North Carolina, Chapel Hill;
Roger T. Bannerman, Wisconsin Department of Natural Resources; Derek B. Booth, Stillwater Sciences,
Inc.; Richard R. Horner, University of Washington, Seattle; Charles R. OMelia, Johns Hopkins University;
Robert E. Pitt, University of Alabama; Edward T. Rankin, Midwest Biodiversity Institute; Thomas R.
Schueler, Chesapeake Stormwater Network; Kurt Stephenson, Virginia Polytechnic Institute and
State University; Xavier Swamikannu, California EPA, Los Angeles Regional Water Board; RobertG. Traver, Villanova University; Wendy E. Wagner, University of Texas School of Law; William
E. Wenk, Wenk Associates, Inc.; LauraEhlers (Study Director), National Research Council.
This report brief was prepared by the National Research Council based on the committees
report. For more information or copies, contact the Water Science and Technology Board at (202) 334-
3422 or visit http://nationalacademies.org/wstb. Copies ofUrban Stormwater Management in the United States
are available from the National Academies Press, 500 Fifth Street, NW, Washington, D.C. 20001; (800) 624-
6242; www.nap.edu.
Permission granted to reproduce this brief in its entirety with no additions or alterations.
2008 The National Academy of Sciences
from roofs in rain barrels, tanks, or cisterns;
the use of permeable pavement; the creation of
inltration trenches, into which stormwater can
seep or is piped; the planting of rain gardens on
both public and private lands, and the planting of
swales along the roadside that capture and treat
stormwater.
The report recommends that nonstructural
stormwater control measures be considered rst
before structural practices, because their use
reduces the reliance on and need for structuralmeasures. The report discusses the characteristics,
applicability, goals, effectiveness, and cost of
nearly 20 different broad categories of stormwater
control measures, organized as they might be
applied from the roof top to the stream.
There is an opportunity to retrot urban areas
with stormwater control measures. Promoting
growth in these areas is a good thing because it
can take pressure off the suburban fringes, thereby
preventing sprawl, and because it minimizes the
creation of new impervious surfaces. However, it
can be more expensive because there is existinginfrastructure and limited availability and
affordability of land. Both innovative zoning
and development incentives, along with careful
selection of stormwater control measures, are
needed to achieve fair and effective stormwater
management in these areas.
Data on Stormwater Discharges
Thanks to a 10-year effort to collect and
analyze monitoring data from municipal separatestorm sewer systems nationwide, a lot is known
about the quality of stormwater from urbanized
areas. Residential land use has been shown to be
a relatively smaller source of many pollutants,
but it is the largest fraction of land use in most
communities, typically making it the largest
stormwater source on a mass pollutant discharge
basis. Freeway, industrial, and commercial
areas can be very signicant sources of heavy
metals, and their discharge signicance is
usually much greater than their land area
indicates. Construction sites are usually the
overwhelming source of sediment in urban areas,
even though they make up very small areas of
most communities. These results come from
many thousands of storm events, systematically
compiled. These data make it possible to
accurately estimate the concentration of many
pollutants for any given storm.
This trafc island has a bioinltration system to capture water. Photo courtesy Villanova Urban Stormwater Partnership.